Clinical MRI (magnetic resonance imaging) is currently experiencing a strong trend towards high field strengths because image signal-to-noise ratio (SNR) can scale up to linearly with field strength. At magnetic fields of about 3 Tesla or more, one problem that must be addressed is non-uniformity of the transmitted RF field (commonly denoted as B1+ or RF+). Non-uniformity in B1+ may cause signal levels and, more importantly, image contrast to vary within an image, making interpretation and quantification difficult.
Uniform treatment of spins is essential during contrast preparation and imaging excitation. Non-uniform B1+ transmission may produce, however, spatially varying flip-angles. This, in turn, may cause intensity and contrast to be non-uniform, and may complicate quantitative imaging.
Accordingly, there is a need for methods and systems that can compensate for non-uniformity of the MRI excitation field B1+ and thereby minimize or reduce variations in intensity and contrast across MRI images.